The conventional stretch blow molding process starts with the fabrication of an object called a “preform.” The preform is of an elongated shape reminiscent of a test tube, having a substantially cylindrical body with an internal cavity defined by one closed end and one open end which communicates with the cavity. The open end of the preform may also be provided with external threading, a shoulder or rim, or other such features generally acting in concert with a sealing or closure means.
Most commonly, the preform will be fabricated by injection molding, using equipment and techniques known to the art of plastics molding. The fabrication of the open end of the preform is generally configured so as to be fundamentally completed in the injection molding step, so that the open end of the preform is in essentially the same configuration as the mouth of the finished container.
Once the preform is fabricated, it must be pre-heated. The pre-heating process is accomplished generally by the use of ovens, radiant heaters, hot-air jets, or other such methods. Preferably, the portion of the preform near the open end is not heated, so as to maintain the shape and structural integrity of the threads et al. which have been disposed at said open end. The preform is heated until it reaches the glass transition temperature for the particular kind of plastic from which it is fabricated, at which point it softens and becomes mechanically workable.
At this point, the preform is ready for molding. The preform is substantially enclosed within a mold, which is generally composed of three segments (a bottom and two sides) which are locked together very tightly. The mold assembly is generally provided with an opening such that the tubular portion of the preform is disposed so as to be within the mold, while the open end of the preform (i.e. the mouth portion) is disposed without. The mouth portion is not deformed or otherwise altered while the rest of the preform is deformed during subsequent steps in the process. The inside of the mold is configured so as to be a reverse image of the container from which the preform is ultimately to be produced.
Once the mold is closed about the preform, the inflation step is commenced. Air is employed as the working fluid, and is injected under very high pressure into the preform through its open end, causing the softened preform to expand until it conforms to the surface defined by the inside face of the mold. The air may be heated to facilitate the deformation of the preform. Once the preform has been fully inflated to the form defined by the mold cavity, the pressurized air within is released; the container is now finished. The mold segments are withdrawn from about the container and the container is removed from the machine. At this point, the machine is reset to begin the forming cycle anew with another preform. The container just produced will then generally proceed to be washed, filled, sealed, and packaged for distribution.
The prior art process is disadvantageous in several respects. Most importantly, it requires a very large amount of energy to carry out. As air is used as the working fluid, to properly carry out the inflation step it must be supplied at extremely high pressure to compensate for its compressibility. In many operations, this means that the air must be compressed to a minimum pressure of approximately 25 bars, requiring a large amount of energy and generating a great deal of waste heat. Usually, much of this heat dissipates into the surroundings. In sum, this means that a continuous source of a large amount of energy is required to successfully blow-mold plastic containers according to the technique known in the prior art.
The prior art process is also disadvantageous in that the production volumes that may be realized are limited by the structure of the molding apparatuses that must be employed. The process of the prior art employs a mold which is comprised of several segments. These segments are most commonly machined from solid blocks of aluminum, and as such often quite ponderous and unwieldy.
When the mold segments are brought together around the preform, they must be clamped together forcefully, then released when the inflation step is complete and moved out of the way so that the container may be removed and the molding process repeated. This slows down the operation of a blow molding machine and increases the time for one molding cycle to be completed (a.k.a. “cycle time”), reducing the overall output of each blow molding machine so employed.
Furthermore, the process is disadvantageous in that it requires a complete mold of the external surface of the container. Such molds must generally be machined from solid blocks of metal, as mentioned above, to achieve the required degree of physical robustness for use in a blow-molding operation. Being molds, they must also by definition include every surface feature of the finished container, and be machined to a very high degree of surface finish to avoid any defects in the mold from being transferred to the surface of the containers it produces. The mold segments must also fit together extremely closely, so as to avoid any leakage (a.k.a. “flashing”) of the plastic between the mold segments or loss of pressure during the expansion step. The high pressures, tight tolerances; and large production runs involved in a blow-molding operation can quickly wear a mold assembly to the point that it is no longer usable for forming containers, requiring refinishing or replacement.
Thus, a properly-constructed mold requires several large blocks of solid metal, into which the exact form of the finished container must be machined within extremely tight tolerances and with a very high quality of finish. This is disadvantageous in that machining objects to such fine tolerances usually requires a considerable amount of time and expertise on the part of the machinist, which increases the cost of implementing this method of fabrication.
There have been attempts in the prior art address each of these problems. Most notably, US application 2006/0097417 described a method for the fabrication of containers, in which a plastic preform was inflated by the use of a fluid, either liquid or gas, under high pressure. The preforms were permitted to expand freely, producing containers having a teardrop shape.
This process is disadvantageous, in that the only control over the deformation of the preform or the form of the container so produced is achieved by the uneven pre-heating of the preform. While some control can be exercised over the broad form of the containers, the containers produced by this method are all still essentially of the same teardrop shape. Any forming of the container beyond this required an additional step where a tool was pressed into the container to deform it, performed subsequent to the inflation step and prior to the filling step.
It is accordingly an object of the invention to provide a process for the fabrication of a container which does not require large amounts of energy, cumbersome and expensive mold tooling, or time-consuming additional steps to produce a useable container.
According to a first aspect, the invention is directed to a method for the fabrication of a container, comprising the steps of providing a preform, said preform being substantially tubular in form and being provided with a closed end, a cavity, and an open end communicating with said cavity; positioning at least one restriction device relative to the preform so as to constrain expansion in at least one restriction zone; and injecting an incompressible fluid of a pre-determined volume into the cavity of the preform via the open end, provoking the preform to plastically deform by expansion, said preform expanding freely in at least one expansion zone outside said at least one restriction zone.
This method is advantageous as compared to the methods of the prior art, as it requires much less energy to carry out than the known methods. First, in any blow-molding process, the working fluid (whether compressible or incompressible) must be brought up to a sufficient pressure to effect the expansion of the preform. In the prior art, the working fluid is a gas, usually air. Compressing air to a sufficient pressure to mold a preform requires a large amount of energy and also generates a great deal of waste heat. In the present invention, the working fluid is an incompressible fluid, which requires much less energy to bring up to the required pressure than a compressible fluid. This may be accomplished by the use of pumps, which are well-known in the art, readily available, and easily adapted to high-volume, continuous service.
Furthermore, this invention is advantageous in that it does not require the implementation of a full multi-segment mold assembly, as in the prior art, to define the ultimate form of the containers it produces. Instead, the final form of the containers is defined by the volume of incompressible fluid injected into the preform to expand the preform, and the localized limitation of the preform's expansion by at least one restriction device.
During the injecting step, the preform will expand as fluid is injected into its cavity via the open end. The restriction zones serve to locally constrain this expansion: the preform will expand uniformly until its outer surface meets the restriction device. At this point, the outer surface of the preform will conform to the restriction zone as defined by the restriction device, and the expansion of the preform into the expansion zones will increase to compensate. By strategically positioning at least one restriction device, the preform may be expanded into a completed beverage container without fabricate and employ a full mold assembly.
The absence of a full multi-segment mold assembly, and the steps for closing it about a preform and opening it to remove the finished container, thus makes the method of this invention faster and more economical to practice than the method known to the prior art.
Also, the absence of a full mold assembly reduces the cost of manufacturing and maintaining the proper tooling required to carry out the process. Rather than manufacturing the mold segments from solid blocks of metal, it is only necessary to fabricate a restriction device or devices. These restriction devices may be configured so as to be much smaller than a full multi-segment mold assembly, possibly fabricated from plates rather than blocks, or from less-expensive materials. Such restriction devices are faster, cheaper, and easier to fabricate, and therefore less costly to fabricate and replace.
According to another feature, after the step for providing the preform, the method includes a step for stretching said preform along a longitudinal axis of said preform.
This facilitates the longitudinal deformation of the preform during the injecting step, promoting uniform deformation of the preform and, as a result, realizing consistent wall thickness and physical properties along the surface of the resultant beverage container. In this way, a greater variety of containers may be produced, while still maintaining consistent structural integrity and uniformity of said containers.
According to still another feature, said pre-determined volume of incompressible fluid injected into the preform during the injecting step is sealed into the container.
This is advantageous in that, if the working fluid used to expand the container is also the fluid which the container is meant to eventually contain, it permits the container to be fabricated and filled at the same time. Combining the steps of expansion and filling thus serve to shorten the process for packaging a liquid product and reduces the amount of equipment needed to carry out the process, thereby lowering the costs incurred by the operator.
According to still another feature, at least one restriction device is a label.
This is advantageous in that it permits the steps of forming the container and labeling it to be combined. This reduces the number of steps required to produce a formed and filled container, yielding faster and more economical output from a production line embodying the invention as compared to one according to the prior art.
According to still another feature of the invention, the invention is further characterized in that prior to the step for injecting a pre-determined volume of an incompressible fluid, the method includes an additional step for pre-heating at least a portion of the preform.
This is advantageous in that when the preform is sufficiently pre-heated, it will become more readily disposed to plastic deformation. This permits the preform to deform to a greater degree during the injecting step than would be possible without such pre-heating. In this way, a greater variety of beverage containers may be manufactured with the process of the present invention than otherwise, thereby increasing the flexibility of the present invention.
According to still another feature, the preform is divided into a plurality of regions, the pre-heating of each region being independently controlled.
This is advantageous in that it permits the preform to be pre-heated to a greater or lesser degree according to the degree of deformation desired in any one particular area. In this way, the amount of total energy used to pre-heat the preform may be minimized, as the pre-heating is only performed where it is necessary, and only to the degree required to meet the requirements of the particular application at hand. In this way, the flexibility that is realized with the addition of a pre-heating step may be realized in a way which is as energy-efficient and cost-effective as possible.
According to a second aspect, the invention is directed to an apparatus for the fabrication of a container, comprising a means for injecting an incompressible fluid of a pre-determined volume into a cavity of a preform via an open end, said preform being substantially tubular in form and provided with a closed end, said open end communicating with said cavity; and at least one restriction device, said at least one restriction device defining at least one restriction zone; wherein said at least one restriction device is disposed relative to the preform so that upon injection of said incompressible fluid of a predetermined volume into the cavity of the preform, the expansion of the preform is constrained within the at least one restriction zone and free within at least one expansion zone outside said at least one restriction zone.
Using at least one restriction device, rather than a full multi-segment mold, reduces the time required to mold a container in that it reduces the time required to prepare the machine to form the preform.
In addition, energy consumption is reduced, as the use of an incompressible fluid to form the container requires less energy to bring to proper working pressure than air or other compressible fluids. In this way, considerable energy savings are realized while at the same time improving output and lowering total cost per unit produced, relative to apparatuses known to the prior art.
According to an advantageous feature, the apparatus comprises means for stretching the preform along a longitudinal axis of said preform.
Absent the use of a stretching means, the natural tendency of the deforming preform is to expand outward at the same rate in all directions. This means that for containers which are longer than they are wide, the expansion of the preform may not be appropriate at every location on the preform's surface, resulting in containers with uneven wall thickness
The usage of a stretching means promotes the even deformation of the preform into a tall container, with even wall thickness and, by extension, consistent physical properties across its surface. In this way, the apparatus may be used to fabricate a wider range of containers, thereby increasing the apparatus' flexibility in operation.
According to another feature, at least one restriction device is disposed coaxially to a longitudinal axis of said preform so as to restrict the expansion of said preform in a radial direction.
This is advantageous in that a restriction device so configured will constrain the radial expansion of the preform, and thus the radius of the containers formed therefrom, over the portion of its surface that defines a restriction zone. In this way, then, the radius of a finished container may be defined at one or several regions while the rest of the preform freely expands. One may thereby fabricate a greater variety of containers, and with greater control over their dimensions and attributes.
According to another feature, at least one restriction device is a label.
This is advantageous in that an apparatus so configured will produce containers which are fabricated, and labeled in one step. This increases the speed and output of a bottling operation, as the time to transfer a container between a fabrication step and a labeling step is eliminated. The fabrication process is thereby rendered faster, more efficient and more cost-effective.
According to still another feature of the invention, said at least one restriction device comprises a tube, disposed about the preform so as to be coaxial with said preform's longitudinal axis and restrict the expansion of said preform in the radial direction.
This is advantageous in that it produces elongated containers with a substantially circular cross-section, a form which is desirable for a beverage container. Such a tube may, in some embodiments, be fabricated from ordinary pipe. This permits the apparatus to be employed without the expense of fabricating a full multi-segment mold. Thus, the output of the apparatus embodying the invention is further increased while being rendered more economical.
According to still another feature, at least one restriction device is disposed perpendicularly to a longitudinal axis of said preform, thereby restricting the expansion of said preform in the longitudinal direction.
This is advantageous in that a restriction device so configured will constrain the longitudinal expansion of the preform, and thus the length of the containers formed therefrom, over the portion of its surface that defines a restriction zone. In this way, then, the length of the finished container may be defined at one or several regions, while the rest of the preform is permitted to expand freely. In this way, then, the restriction devices may be configured so as to yield a finished container with the required dimensional attributes while still expanding freely elsewhere. One may thereby fabricate a greater variety of containers, and with greater control over their dimensions and attributes.
According to another feature, said at least one restriction device comprises a base plate disposed so as to define a bottom end of the container.
This is advantageous in that, depending on its size and intended application, it may be desirable for the container to have a specific, defined shape at its base. Utilizing a restriction device in the form of a base plate will produce a container whose form is otherwise defined by the volume of incompressible fluid injected into the preform, but whose base portion is as defined by the base plate. This renders the method more flexible, permitting its advantages to be realized in a greater number of applications.
According to still another feature, the apparatus comprises a plurality of base pins, said base pins being retractably disposed and arranged perpendicularly to said longitudinal axis.
This is advantageous in that the preform expands around the base pins, forming a plurality of petaloid lobes in the bottom of the beverage container so formed. The pins are retractably mounted so that the container may be removed after forming is complete. Such petaloid shapes are employed on the bottoms of containers holding carbonated liquids or other such substances under pressure, as they are highly resistant to pressure and give the container a good degree of structural rigidity and strength. Through this feature of the invention, a container having a petaloid base may be formed without the use of a full multi-segment mold, and without the accompanying expense of its fabrication. In this way, the advantages of a petaloid base may be realized with a minimum of cost and adaptation, and with the increased efficiency and rate of production that the other features and aspects of the present invention entail.
According to still another feature, at least one restriction device is disposed obliquely to a longitudinal axis of said preform.
This is advantageous in that it permits the fabrication of containers where one region of its surface is oblique to the open end, said region being substantially defined by the restriction device. In this way, the invention is rendered more flexible and capable of producing containers in a greater variety of forms.
According to a third aspect, the present invention concerns a beverage container fabricated by a method as described above.
This is advantageous in that such a beverage container embodies the advantages of the method by which it is fabricated. The beverage container will thus be better adapted to its intended use and less expensive than comparable beverage containers produced by methods known in the prior art.